Two-stage hammer mill

ABSTRACT

A two-stage rotary hammer mill having first and second rotary hammer mill stages mounted on a common drive shaft and driven together in unison, the first stage producing a semiground product, and the second stage receiving the semiground product and producing a finely ground product, in which the second stage incorporates blower means drawing air through the system and thereby ensuring free flow of product therethrough, the two stages being arranged in a common housing, and product released from the screen of the first stage being collected in a generally annular space and directed into a conduit and delivered to the second stage around the central axis thereof.

United States Patent Palyi 1 Feb. 22, 1972 [54] TWO-STAGE HAMMER MILLFOREIGN PATENTS OR APPLICATIONS [72] Inventor: Lesli Palyi, D n ill nCanada 1,024,781 2/1958 Germany ..241/ Assigneez Nicholas Pora 2 1 GreatBritain [22] Filed: July 1969 Primary Examiner-Andrew R. Juhasz [21]Appl. No.: 840,691 Assistant Examiner-Michael Koczo, Jr.

A1t0rneyGeorge A. Rolston [30] Foreign Appl1cat1on Prlorlty Data [57]ABSTRACT .l l 17,1968 G tB 't ..34,052 68 u y tea n am I A two-stagerotary hammer m1ll havmg first and second rotary [52 u.s.c1 ..241/55241/154 hamme Stages mumed a Shah and 51] Int. (:1. ..B62c 13/04 drive"together in unison the first Stage Producing a [58] Field of Search..241/55, 56, 50, 51, 45, 154, semiground Product, and the Second stagereceiving the 241/43, 73, 188, semiground product and producing a finelyground product, in which the second stage incorporates blower meansdrawing air [56] References Cited through the system and therebyensuring free flow of product therethrough, the two stages beingarranged in a common UNTED STATES PATENTS housing, and product releasedfrom the screen of the first 1 ,572,722 2/1926 .lacobsen ..241/55 stagebeing collected in a generally annular space and directed 1, 1 Praterinto a conduit and delivered to the second stage around the 2,494,1071/1950 Ryan "24 H188 R central axis thereof. 2,679,788 6/1954 Skardal..241/73 3,037,712 6/1962 l-losokawa ..24l/56 10 Claims, 6 DrawingFigures Outlet 2 Product Air PATENTEDrsazz m2 SHEET 1 0f 3 Outlet FIGJInventor k LESLIE FALYI by: ywu. m.

PATENTEDFEBZZ I972 3.643 .879

SHEET 2 OF 3 Inventor LESLIE PALYI by: yeayefl M1.

PATENTEDFEB 22 ten SHEET 3 BF 3 lnventbr LESLIE PALYI by: 9ea gyeag. M.

TWO-STAGE HAMMER MILL This invention relates to a hammer mill providedwith two separate grinding stages operating simultaneously on a commondrive shaft.

Single stage hammer mills are well known, in which the product to beground is subjected to a flailing motion from a large number ofso-called hammers or bladelike members carried on a central rotor. Insuch mills, it is common to experience a relatively high rate of wear,and the degree of grinding is not always consistent, especially when asubstantial reduction in particle size is required in a single stage.

Furthermore, in such single stage hammer mills, if it is desired toobtain a consistent finely ground product, it is necessary that a finescreen should be employed, which obviously slows down the rate of flowof material therethrough. As a result, the speed with which a relativelycoarse material can be ground is substantially restricted, and in fact,the rate of output, when using such a fine screen is quite inefficientand uneconomical. If it is attempted to speed up the input of v coarsematerial, then the usual result has been to completely clog the screen.

In addition, the design of the hammers or flail like members within thehammer mill which are suitable for grinding coarse material may notalways be suitable for grinding fine material, and vice versa. As aresult, the maximum efficiency is seldom obtained.

One of the factors effecting the rate of flow of the fine materialthrough a fine screen is the amount of airflow that can be achievedthrough the mill. Such finely divided material will seldom move underthe influence of gravity, or even by the centrifugal forces appliedwithin the mill. In fact, in order to move substantial masses of finelydivided powdered material in the circumstances, it is found to beessential to provide for a substantial airflow so as to entrain thepowdered material and clear the screen more rapidly.

With a view overcoming these various disadvantages the invention seeksto provide a hammer mill having two stages consisting of a coarse grindfollowed by a fine grind. The two rotor portions of the hammer mill arearranged spaced apart from one another on a common drive shaft, mountedwithin a common housing, and separated by a partition, the first stageproviding a relatively coarse reduction of the material through arelatively coarse screen, after which the coarsely ground material flowsaround the partition into the second stage in which it is finely groundpasses through a fine screen. Substantial quantities of air areentrained in the process, and the use of a two-stage rotor system isfound to procure increased airflow therethrough by centrifugal action.Where extra heavy material is to be ground, additional air is admittedbetween the first and second stages, and the spacing between the firstand second stage rotors on the drive shaft is increased, and an enlargedpassageway is provided for flow of the coarsely ground material to thesecond stage rotor.

Accordingly it is an objective of the invention to provide two hammermills on a common operating shaft, together with means for continuouslyand automatically conveying the semiground product from the first stageto the second stage, thereby substantially reducing the rate of wear andensuring a more uniform end product and providing a greater reduction inparticle size.

A further objective of applicants invention is to provide a two-stagehammer mill, the semiground product being moved from the first stage tothe second stage by pneumatic means.

A further objective of the invention is to provide a two-stage hammermill in which the second stage is provided with fan means whereby air iscontinually drawn through the first stage thereby entraining thesemiground product, and is blown directly out of the outlet end of themill, entraining such ground end product with the mass of air beingmoved by such fan means for delivery in any desired manner.

More particularly, it is an objective of the present invention toprovide a two-stage hammer mill having the foregoing advantages in whichproduct is introduced .to the rotor means in the first stage from oneside thereof, and in which the semiground product exiting from the firststage is introduced to the second stage more or less around the axis ofthe common drive shaft and into a central region of the second stagerotor, and passes outwardly through such second stage rotor undercentrifugal force and substantial airflow, induced by such second stagerotor.

More particularly, it is an objective of the present invention toprovide a two-stage hammer mill having the foregoing advantages which isparticularly adapted for heavy duty grinding in which air is introducedto the first stage, and in which conduit means are provided between theoutput side of the first stage, and the axial input side of the secondstage, and in which additional air is introduced into such productconduit.

More particularly, it is an objective of the present invention toprovide a two stage hammer mill having the foregoing advantages in whichthe second stage rotor is of greater diameter than the first stage rotorthereby providing increased peripheral speeds of the grinding members inthe second stage.

The foregoing and other objectives will become apparent from thefollowing description of a preferredembodinient of the invention whichis given here by way of example onlywith reference to the followingdrawings in which like reference devices refer to like parts thereofthroughout the various views and diagrams and in which;

FIG. 1 is a side elevational view of a two-stage hammer mill accordingto the invention, with the principal features thereof sectioned anddesigned for high volume use with lighter more easily ground feed;

FIG. 2 is a greatly enlarged side elevational view of the second stagerotor of the mill shown in FIG. 1;

FIG. 3 is an end elevational view of the rotor member shown in FIG. 2;

FIG. 4 is an enlarged end elevational view of a hammer blade member.

FIG. 5 is a sectional side elevational view of an alternative embodimentof the invention particularly designed and adapted for medium dutyoperation, and,

FIG. 6 is a sectional side elevational view of a still furtherembodiment of the invention particularly designed and adapted for heavyduty use.

Referring now to FIG. 1 the invention will be seen to comprise a base 10having bearings 11 carrying a shaft 12 driven by any suitable means (notshown). A stationary rotor housing 13 is supported by any suitable means(not shown), and is divided by partition 14 into first and second rotorchambers, communicating through a central circular port formed in partition 14 and indicated as 15. A product inlet opening indicated as 16in housing 13 and is provided with an airflow regulating vane 17adjustably mounted therein. A product outlet port 18 communicates withthe second rotor chamber for delivery of finely ground producttherefrom.

The first rotor stage consists of a rotor member 20 preferably beingprovided with three separate disc portions 21 member 20 being attachedto shaft 12 by any suitable means such as a retaining member. Long andshort hammer blade members 23 and 24 (which are seen edge on in FIG. 1,and are shown in more detail in FIG. 4), are mounted side by side withone another on mounting bolts 25. It will be understood that blades 23and 24 are of different lengths although being substantially of theshape shown in FIG. 4 and are mounted alternately along respective bolts25 in spaced apart locations around rotor member 20, there being in allapproximately six such bolts 25 carrying respective groups of blades 23and 24 in this preferred embodiment. The annular retaining wall 26 isfastened within housing 10 closely adjacent the path of the rotor blades23 and 24 as shown, and an annular screen 27 is supported between member26 and housing 13 for screening the semiground product from the firstrotor stage and permitting the same to escape radially outwardlytherefrom as soon as the same passes the mesh of such screen 27. Housing13 defines a substantial annular space indicated generally as 28 aroundscreen 27 for the purpose of permitting free passage of ground producttherefrom, and space 28 in turn communicates with the disc shapedpassageway, lying between member 26 and partition member 14, therebyproviding free communication of air and entrained semiground product,along the pathway indicated by the arrow A through the port and into thesecond stage.

The second stage of the present invention consists essentially of asecond hammer mill assembly generally similar to the hammer millassembly in the first stage although somewhat larger, together with acentrifugal fan for drawing air through the first stage and thenentraining the product and blowing the same out of the outlet 18. Boththe hammer mill assembly and the centrifugal fan of the second stage aresupported on the same rotor member 29 which is preferably provided withtwo separate disc portions 30 and 31 respectively, disc member 31 beingprovided with a central annular opening 32 through which semi orpartially ground product from the first stage may enter from port 14. Inthis preferred embodiment, six separate fan blades 33 are mountedbetween disc members 30 and 31 arranged therearound in a radial manneras shown in FIGS. 2 and 3. In addition to such fan blades 33 there areprovided, in this preferred embodiment, six groups of hammer blademembers 34 and 35, blade 34 and 35 being of different lengths, althoughbeing substantially of the shape shown in FIG. 4. Blade members 34 and35 are mounted side by side alternately on mounting bolts 36. An annularscreen member 37 is supported within housing 13, closely adjacent to thecircumferential path of blades 34, to permit the escape of groundproduct therefrom, and housing 13 further defines a substantial annularspace indicated generally as 38 extending around the exterior of screenmember 37, for permitting free flow of ground product entrained with airfrom screen 37 therearound and out of outlet 18.

In operation, product is introduced through the inlet 16, and enters thehousing 13 to one side of the primary rotor 20, which is rotating athigh speed, thereby causing such product by centrifugal force to flowoutwardly between the hammer blade members 23 and 24, and is ground bysuch hammer blade members 23 and 24 against the mesh screen 27. Asstated, screen 27 is relatively speaking coarse in relation to theproduce being ground, whereby only a semigrinding or coarse reductiontakes place after which the semiground product is free to pass throughthe screen 27 into the annular passageway 28. Since both rotors and 29are mounted on a common shaft, rotor 29 will be rotating at the samespeed at rotor 20, and the fan blade means 33 on the rotor 29 will causea relatively massive air flow therethrough and outwardly through productoutlet 18. Air expelled by this means can of course enter through theproduct inlet 16, and as a result there is a continual relativelymassive air flow through inlet 16, and around the rotor 20, through themesh screen 27 into the annular space 28 and thence through the opening15 in partition 14 and out of outlet 18. Such airflow will entrain withit the semiground material exiting from the screen 27 into the space 28and such material will be carried by such air in the direction of thearrow A passing through the disc-shaped passageway between the rotor 20and the partition 14 until it passes through the central axial opening15 into the second stage. At this point, due to the impeller action ofthe fan blades 33, the air and entrained semiground product passesthrough the axial opening 32 in the rotor disc member 31 and is thenexpelled outwardly by centrifugal force and combined airflow between fanblades 33 and hammer blade means 34 and 35. At this stage, suchsemiground product is then subjected to further fine grinding betweenthe blades 34 and 35 and the fine screen 37, after which, as soon as thesame passes through such fine screen 37 it enters the annular space 38and exits from the housing 13 through outlet 18, being entrained withthe mass airflow exiting therefrom.

According to a further embodiment illustrated in FIG. 5, where a mediumweight of product is to be ground, the design of the housing 13 andpartition 14 may be modified to ensure a somewhat freer product flowfrom the first stage to the second stage, and in addition, additionalair inlet means are provided in the housing to permit the introductionof additional air between the first and second stage.

Thus as shown in FIG. 5, the housing 13 is provided with a product inlet16, and a primary air inlet means 40 permits the introduction of airsomewhat closer to the first stage, than in the embodiment of FIG. 1,thereby ensuring that the incoming unground product is fully aerated andflows freely. The design of the first and second stage rotors 20 and 29is essentially the same as in the embodiment of FIG. 1, with theexception that they are spaced somewhat further apart on the drive shaft12 in order to permit freer flow of air and entrained semiground productfrom the first to the second stage. In addition, the partition member 41is provided, corresponding to the partition member 14 of FIG. 1,partition 41 being of generally frustoconical saucer-shaped constructionand provided with lips 42 defining the opening 15 therethrough, the lips42 opening directly into the central axial spacing around rotor 29whereby to ensure that the air and entrained semiground product passesdirectly into such central axial region and is completely groundthereafter. The annular spacing 28 is provided around the screen 27,and, since the product being ground in this embodiment will be somewhatheavier, the majority of such semiground products will fall under theinfluence of gravity to the lower region of such annular space 28. Inorder to ensure free and continuous flow of air and entrained semigroundproduct from such annular space 28, a secondary air inlet 43 is providedadjacent the lowermost position of the annular spacing 28 wherebyadditional air is introduced into the system, such additional air beinginducted by the fan blades 33 and the rotor member 29. As in the case ofthe embodiment of FIG. 1, the screen 37 of the second stage is ofsomewhat greater diameter and width than the screen 27 of the firststage, whereby to provide a greater screen area for the passage of thefinely divided material without plugging of the screen at any particularlocationv A product outlet 18 is provided in a somewhat differentlocation for delivery of the finely ground product therefrom.

As is apparent, by means of the embodiment of FIG. 5, the somewhatheavier product and semiground product from the first stage is providedwith a somewhat larger passageway for freer flow of air and entrainedsemiground product, thereby ensuring maximum throughput at all times.

A still further embodiment of the invention is shown in FIG. 6 forheavy-duty use where an even heavier product is to be ground. In thiscase, the housing 13 is separated essentially into two separatecompartments by means of the partition 50, and the primary and secondaryrotors 20 and 29 are spaced still further apart on the drive shaft 12,although again, being of essentially the same design as in theembodiment of FIGS. 1 and 5. In the embodiment of FIG. 6, the screen 27of the primary stage extends between the wall of the housing 13 and thepartition member 50 thereby completely enclosing the primary rotor 20,the annular passageway 28 extending around the exterior of screen 27,and communicating at its power end with the product delivery duct 51.Duct 51 is located at the lower end of the housing 13 sincesubstantially all of the heavy semiground product will quickly passunder the influence of gravity to the lower portion thereof. As in thecase of the embodiment of FIG. 5, a primary air inlet 40 is providedadjacent to the product inlet 16, thereby ensuring free flow of ungroundproduct into the housing 13, to one side of the rotor 20 as shown.

A secondary air inlet indicated as 52 is provided commu nicating withthe semiground conduit 51, permitting the in take of additional air toentrain and carry the semiground product upwardly through the opening 32and into the central region of the secondary stage rotor 29. It will benoted that an additional partition 53 is provided in this embodimentsubstantially enclosing the secondary stage rotor 29, and the secondarystage screen 37 extends between the sidewall of the housing 13 and thepartition 53. A product outlet 18 communicates with the annular space 38for delivery of finely ground product therefrom.

In the operation of the embodiment of FIG. 6, the unground product isintroduced into the product inlet 16 and flows under the influence ofgravity in through the opening 16a in housing 13, and into the centralregion of the rotor 20 where it is thrown by centrifugal force outwardlybetween the hammer blades 23 and 24 and is ground to a semigroundcondition against the screen 27. As soon as the semiground materialpasses through the screen 27, it is drawn downwardly to the lower regionthereof into the product conduit 51 by means of air inducted through theprimary air inlet 40 and product inlet 16 under the influence of the fanblades 33 of the secondary stage motor. At this point, additional air iscontinually drawn in by the fan blades 33 through the secondary airinlet 52 and ensures that all such semiground product is completelyentrained and drawn upwardly through the conduit 51, and through theopening of the partition 53 and through the opening 32 in the discmember 31 of the rotor 29 and into the central region of the rotor2 9where it is thrown outwardly by centrifugal force and is ground againstthe screen 37 by means of the blades 34, 35. The product then passesaround the annular space 38 out of the product outlet 18.

By this means, it is found that the power requirements of the system forreducing even relatively course material to a fine grind are greatlyreduced, for a given product output in comparison with the powerrequirement of known systems, and, in addition, the rate of wear on themoving parts is greatly reduced, and the possibility of causingundesirable overheating of the product during grinding is also reduced.

The foregoing is a description of the preferred embodiment of theinvention which is given here by way of example only.

What I claimed is:

1. A two-stage rotary hammer mill, for continuous grinding of a productin two steps, the first grinding stage reducing said product to apredetermined semiground condition, and the second stage reducing saidsemiground product to a more finely ground end product, said apparatuscomprising:

housing means enclosing first and second grinding stages and having aninlet opening in said first stage and an outlet opening in said secondstage;

partition means within said housing means separating said first andsecond stages;

a first rotary hammer mill means and mill screen means therearound,located in said housing means and spaced therefrom, and adapted toreduce said product to said semiground condition, and deliver samebetween said mill screen means and said housing means;

a second rotary hammer mill means in said second stage coaxial with saidfirst hammer mill means and adapted to receive said semiground product,and further reduce the same to said finely ground end product;

drive means for said first and second stage hammer mill means; anannular product outlet space around said first hammer mill means;

2. The apparatus as claimed in claim 1, including a common housing forsaid first and second stages; and

a drive shaft extending into said housing, and said first and secondstage hammer mill means mounted in spacedapart relation on said driveshaft. 3. The apparatus as claimed in claim 1, including an annularproduct outlet space around said second hammer mill means.

4. The apparatus as claimed in claim 1, wherein said second stageincludes at least two spaced-apart disc portions mounted on a centralhub;

hammer members swingably mounted between said disc portions, and,

fan blade means mounted between said disc portions.

5. The apparatus as claimed in claim 4, including an annular productinlet opening in one of said disc portions at least, arranged to admitsemiground product around said hub member, said product thereafterpassing between said disc members for grinding.

6. The apparatus as claimed in claim 1, including primary air inletmeans associated with said product inlet opening in said housing.

7. The apparatus as claimed in claim 1, including secondary air inletmeans communicating with said housing means for communicating additionalair between said first and second stages.

8. The apparatus as claimed in claim 1, wherein each said stagecomprises at least two disc members mounted spaced apart from oneanother on a hub member, hammer members swingably mounted between saiddisc members for rotation in unison therewith, and annular screen meansextending around and spaced from said hammer members.

9. The apparatus as claimed in claim 1, wherein said partition means isshaped in the form of a shallow cone with the apex thereof directedtowards said second stage, and a circular product opening formed in saidpartition around the apex of said cone.

10. The apparatus as claimed in claim 1, including air inlet meanscommunicating with said annular space around said first stage to pennitentry of additional air.

1. A two-stage rotary hammer mill, for continuous grinding of a productin two steps, the first grinding stage reducing said product to apredetermined semiground condition, and the second stage reducing saidsemiground product to a more finely ground end product, said apparatuscomprising: housing means enclosing first and second grinding stages andhaving an inlet opening in said first stage and an outlet opening insaid second stage; partition means within said housing means separatingsaid first and second stages; a first rotary hammer mill means and millscreen means therearound, located in said housing means and spacedtherefrom, and adapted to reduce said product to said semigroundcondition, and deliver same between said mill screen means and saidhousing means; a second rotary hammer mill means in said second stagecoaxial with said first hammer mill means and adapted to receive saidsemiground product, and further reduce the same to said finely groundend product; drive means for said first and second stage hammer millmeans; an annular product outlet space around said first hammer millmeans; axial opening means in said partition means for conductingsemiground product from said first stage to said second stage along thecentral axis of the second rotary hammer mill means; product passagewaymeans communicating only between said annular space and said opening insaid partition; and, fan blade means mounted on said second rotaryhammer mill means for rotation therewith to draw air through said firststage and through said axial opening into said second stage and impelair out of said outlet thereby ensuring free flow of product throughboth said stages.
 2. The apparatus as claimed in claim 1, including acommon housing for said first and second stages; and a drive shaftextending into said housing, and said first and second stage hammer millmeans mounted in spaced-apart relation on said drive shaft.
 3. Theapparatus as claimed in claim 1, including an annular product outletspace around said second hammer mill means.
 4. The apparatus as claimedin claim 1, wherein said second stage includes at least two spaced-apartdisc portions mounted on a central hub; hammer members swingably mountedbetween said disc portions, and, fan blade means mounted between saiddisc portions.
 5. The apparatus as claimed in claim 4, including anannular product inlet opening in one of said disc portions at least,arranged to admit semiground product around said hub member, saidproduct thereafter passing between said disc members for grinding. 6.The apparatus as claimed in claim 1, including primary air inlet meansassociated with said product inlet opening in said housing.
 7. Theapparatus as claimed in claim 1, including secondary air inlet meanscommunicating with said housing means for communicating additional airbetween said first and second stages.
 8. The apparatus as claimed inclaim 1, wherein each said stage comprises at least two disc membersmounted spaced apart from one another on a hub member, hammer membersswingably mounted between said disc members for rotation in unisontherewith, and annular screen means extending around and spaced fromsaid hammer members.
 9. The apparatus as claimed in claim 1, whereinsaid partition means is shaped in the form of a shallow cone with theapex thereof directed towards said second stage, and a circular productopening formed in said partition around the apex of said cone.
 10. Theapparatus as claimed in claim 1, including air inlet means communicatingwith said annular space around said first stage to permit entry ofadditional air.